Referring to FIG. 1, a peristaltic pump 102 is typically used to deliver either water, or a liquid chemical or mixture, from a source 104 to a receiving device 106 (e.g., a dishwasher, or clothes washer). The peristaltic pump 102 has a rotor 110 (FIG. 2A) with rollers 112 (112-A and 112-B in the example shown in FIG. 2A) that compress a tube 114 as the rotor is rotated. The pump 102 is driven by a motor (not shown in FIG. 1), and liquid is drawn into the tube 114 (also called the tubing) at an inlet 120 and then forced through the tube to an outlet 122 by the rollers of the rotor as the rotor turns on its axis. Operation of the pump 102 is controlled by a controller 130, which typically runs the pump 102 for a fixed or specified amount of time in order to deliver a corresponding amount of product (i.e., the liquid being pumped) to the receiving device 106.
Battery powered peristaltic pumps are inexpensive, and almost all are controlled, so as to deliver a specific amount of product, by controlling the run time of the pump. The run time is typically determined by calibrating the pump. For some pumps, calibration is accomplished by running the pump until a fixed amount of product (e.g., 100 milliliters) is delivered. Then the user programs the pump to deliver a specified multiple of the fixed amount used for calibration. For other pumps, the calibration is accomplished by running the pump until the target amount of product is delivered, and that amount of time is stored in the pump's controller. For such pumps, during normal or production use the pump is run for the same amount of time as was determined during calibration.
Experience has shown that the amount of product delivered by a peristaltic pump decreases as the pump's battery ages. Attempts to modify the pumps's run time based on a measurement of the battery voltage, so as to deliver a constant volume of product, have been largely unsuccessful. The amount of product was found to vary widely, especially from unit to unit of nominally identical pumps (i.e., same model, same type of tubing, etc.). Thus, the volume of product delivered is not well defined by the run time and battery voltage.
It would be beneficial to provide a low cost control mechanism and method, for ensuring that the amount of product delivered by a peristaltic pump remains substantially unchanged despite aging of the pump's battery.